In a rolling bearing, in order to improve the lubricity between an inner raceway surface and rolling elements, or an outer raceway surface and the rolling elements, usually, lubricating oil is supplied into or grease is packed in an annular space formed between an inner race and an outer race. In order to supply lubricating oil or to pack grease in such a space between the inner race and the outer race, or to prevent water, a foreign material, or the like from entering from the outside into the space, a contact type seal, a labyrinth seal, or the like is usually attached to the both axial ends of the annular space so as to hermetically seal or isolate from the outside the space between the inner race and the outer race.
In a double-row self-aligning roller bearing in which two raceway surfaces are formed in the outer periphery of the inner race and one raceway surface configured by a spherical face is formed in the inner periphery of the outer race, when the roller bearing is used under certain conditions, however, there is a case where the rolling elements rotate while being projected from the outer raceway surface. When one of the above-mentioned conventional lubrication techniques is used in such a self-aligning roller bearing, therefore, there arises the possibility that lubricating oil or the grease leaks out to the outside of the bearing.
When a rolling bearing of the grease packed type is used as a rolling bearing to be placed at, for example, a high overhead location or an inner location of an apparatus, it is difficult to conduct lubrication maintenance such as grease additional injection.
As one of countermeasures against such cases, conventionally, a technique is known in which a so-called polymeric lubricant that is obtained by heating and melting, or solidifying a mixture of a polymer, and lubricating oil or grease is packed in a space formed between an inner race, an outer race, and rolling elements (for example, Japanese Patent Publication (Kokai) No. HEI6-50330). In such a polymeric lubricant packed bearing, the lubricating oil or the grease contained in the polymer is gradually released by rotation of the bearing to penetrate between the raceway surfaces of the inner and outer races and the rolling elements, so that a satisfactory lubrication state can be maintained over a long term.
Usually, the polymeric lubricant which is used in such a bearing is obtained by solidifying a mixture of an ultrahigh molecular weight polyethylene resin and lubricating oil or grease. When such a polymeric lubricant is to be packed between inner and outer races of a bearing, a method is usually employed in which the mixture is heated and melted, the mixture in a molten state is filled into the space between inner and outer races of an assembled bearing and rolling elements, and the mixture is then cooled and solidified.
In such a polymeric lubricant packed bearing, the polymeric lubricant is in contact with the rolling elements or the inner and outer races to generate a sliding frictional resistance, thereby producing produces problems in that the rotational torque of the bearing is increased, and that the rolling bearing is self-heated by the sliding frictional resistance and the polymeric lubricant is melted and damaged.
In a countermeasure in which, before shaping of a polymeric lubricant, lubricating oil is poured into a bearing to form an oil film, however, the amount of the lubricating oil to be poured into the bearing must be set to a constant value in order to ensure an adequate thickness of the oil film, and hence a large manpower is required for a step of pouring the lubricating oil. Furthermore, in a roller bearing or the like, particularly, even when an oil film is formed by lubricating oil, the above-mentioned sliding frictional resistance cannot be sufficiently reduced, thereby producing a problem in that required low-torque characteristics cannot be attained.
As a countermeasure against such problems, a method is conventionally known in which, before a polymeric lubricant is packed in a bearing, lubricating oil is poured into the bearing to form an oil film, and a polymeric lubricant is shaped in the presence of the oil film.
In a double-row self-aligning roller bearing, during rotation in an aligned state, leading or lagging usually occurs in the right and left rolling element rows. When, in such a double-row self-aligning roller bearing, a polymeric lubricant is packed in a whole gap formed between the inner and outer races, the right and left rolling element rows are restrained by the polymeric lubricant. As a result, particularly in the use at a high speed, the leading or lagging between the rolling element rows causes a large force to act on the polymeric lubricant, thereby causing the possibility that the polymeric lubricant is damaged.
In order to solve the above-discussed problems in a self-aligning roller bearing, alternatively, a structure may be employed in which a polymeric lubricant between inner and outer races is axially divided to be formed independently respectively for the rolling element rows. As exemplarily shown in an axial section view of FIG. 8, a double-row self-aligning roller bearing has a structure where, between an inner race 1 on an outer periphery of which two raceway surfaces 1a and 1b are formed, and an outer race 2 in which one raceway surface 2a that is arcuate in an axial section is formed, two rolling element rows 3a and 3b which respectively correspond to the raceway surfaces 1a and 1b of the inner race 1, and each of which is configured by a plurality of rolling elements 3 are held by respective cages 4a and 4b. In the double-row self-aligning roller bearing, polymeric lubricants 7 which are separated from each other are disposed to respectively correspond to the rolling element rows 3a and 3b, so that the rolling element rows 3a and 3b can independently rotate (revolve) together with the respective polymeric lubricants 7. Such a structure of a polymeric lubricant packed bearing in which independent polymeric lubricants are disposed respectively for rolling element rows is already known (for example, Japanese Patent Publications (Kokai) Nos. HEI9-14273 and HEI11-280768).
A stable method of producing such a polymeric lubricant packed bearing in which independent polymeric lubricants are disposed respectively for rolling element rows has not yet been established. In the state of the art, therefore, a polymeric lubricant packed bearing having such a structure has not yet been practically used.
Japanese Patent Publication (Kokai) No. HEI9-14273 discloses a method in which rolling elements of rows are inserted with being held in corresponding cages into respective molds that are separately prepared, raw materials of a polymeric lubricant are poured into the molds and then solidified to produce two doughnut-shaped molded products in each of which the cage, the rolling elements, and the polymeric lubricant are integrated to one another, and the molded products are fitted between inner and outer races of a bearing. However, it is very difficult to fit a polymeric lubricant which is previously shaped together with a rolling element row and a cage into a doughnut-like form, between inner and outer races. In a double-row self-aligning roller bearing of the type in which a retaining flange 11 is formed in each of the both ends of the inner race 1 as shown in FIG. 8, particularly, it is substantially impossible to conduct the above-mentioned fitting of the doughnut-shaped molded products because of interference with the retaining flanges 11.
Japanese Patent Publication (Kokai) No. HEI11-280768 discloses a method in which two cages holding respective rolling element rows are incorporated into a bearing while a polymeric lubricant is previously formed integrally with columnar portions that are positioned respectively between pockets, and that hold intervals of rolling elements adjacent in the circumferential direction. However, this method has problems in that a mold which has many small cavities for respectively housing the columnar portions of each cage is additionally required, and also that there is the possibility that the polymeric lubricant is peeled off or damaged by a force which is applied during a process of placing the cage into a bearing and inserting rolling elements into respective pockets.